1. Field of the Invention
The present disclosure relates to a heater used as a heat source of a toner fixing device in a copying machine or the like.
2. Description of the Related Art
In recent years, a heater having a linear heat generator, having a low heat capacity, has been used as a heat source of a toner fixing device in a copying machine, an electro-photographic printer, or the like. A toner fixing device in which such a heater is incorporated has the advantage of achieving power saving and a reduction in wait time compared to a toner fixing device employing a heat roller system, a heat plate system, a flash fixing system, an oven fixing system, or the like.
Examples of such heaters include a heating element of a fixing device described in Japanese Unexamined Patent Application Publication No. 2-157886, and a heating element of a fixing device described in Japanese Unexamined Patent Application Publication No. 9-068877.
The heating element 820 described in Japanese Unexamined Patent Application Publication No. 2-157886 will be described below with reference to FIG. 13. FIG. 13 is a plan view showing the configuration of the heating element 820.
As shown in FIG. 13, the heating element 820 includes a heater body 821a and a heater body holding member 820a. The heater body 821a includes an alumina substrate 821, a heat generator 822 made of silver-palladium (Ag/Pd) that is formed substantially in the center of the surface of the alumina substrate 821 along the longitudinal direction by screen printing in a linear or band-like shape, and a wear-resistant material such as glass. The temperature of a fixing nip part corresponding to the heat generator 822 is maintained and controlled at a predetermined fixing temperature. Using a side wall surface 820k of a horizontally long slot 820b of the heater body holding member 820a as a surface reference K, the heater body 821a is fitted into the slot 820b with a longitudinal side wall surface 821k of the alumina substrate 821 in close contact with the surface reference K, and is integrally attached to and held by the heater body holding member 820a. Owing to the surface reference K, the heat generator 822 can be positioned.
In the fixing device described in Japanese Unexamined Patent Application Publication No. 9-068877, in order to improve the positional precision, the following structure is discussed. The fixing device 911 described in Japanese Unexamined Patent Application Publication No. 9-068877 will be described below with reference to FIGS. 14 and 15. FIG. 14 is a sectional view showing the schematic configuration of the fixing device 911. FIG. 15 is a bottom view showing a heater substrate 922 of the heating element 920 of the fixing device 911.
As shown in FIG. 14, the fixing device 911 includes a fixing film 925, a moving driving means for the fixing film 925, the heating element 920, and a pressure roller 928. The heating element 920 includes a heater support 921 and the heater substrate 922. The heater substrate 922 is a flat plate formed of alumina, aluminum nitride, or the like, and is embedded in the heating element 920. The heating element 920 and the pressure roller 928 are disposed opposite to each other with the fixing film 925 interposed therebetween. As shown in FIG. 15, the heater substrate 922 is provided with a heat generator 923 formed integrally with electrodes 931, and marks 930 for position adjustment of the heat generator. The heat generator 923 and the marks 930 for position adjustment of the heat generator are printed patterns formed by collective printing using the same printing plate.
However, if the positional precision of the linear heat generator is low, toner disposed on a recording material cannot be heated appropriately. In the case of the heating element 820 of the fixing device described in Japanese Unexamined Patent Application Publication No. 2-157886, the positional precision of the heat generator 822 may be deteriorated owing to the processing variation of the heater body holding member 820a and the processing variation of the alumina substrate 821. In the case of the fixing device 911 described in Japanese Unexamined Patent Application Publication No. 9-068877, the heat generator 923 and the electrodes 931 are often covered with a protective layer in order to secure durability and insulation thereof. When a protective layer is formed over the marks 930 for position adjustment of the heat generator, the outlines of the marks 930 for position adjustment of the heat generator may not be clearly visible. In particular, when the protective layer is formed by screen printing, surface roughness due to a mesh of a printing plate is left on the surface, therefore light is scattered, the outlines of the marks 930 for position adjustment of the heat generator are not clearly visible, and highly precise positioning is difficult. Therefore, with such a structure of the heat generator, highly precise positioning cannot be performed easily.